Differential creepage control system for optimizing adhesion of locomotives

ABSTRACT

This invention concerns a creepage control system for locomotives that optimizes adhesion while minimizing wasted energy, rail/wheel wear and shock loading on the drive train. The basis of the invention is to always maintain a small but positive value of the slope of the wheel-rail adhesion creep curve (or differential of adhesion versus creep) for all traction axles of the locomotive through microprocessor control. The value of the differential of adhesion versus creep is used to define an operating window for control and operation of motors continually in the optimum domain when high adhesion is demanded. When, due to a sudden increase in rail contamination, the value of the control function becomes negative, the microprocessor control reduces the generator excitation in stages until the function becomes positive and inside the operating window again. The microprocessor controls a rail cleaning system which is turned on or off depending on the cleanliness of the rail. It also controls a rail sanding system which is turned on or off depending on the magnitude of wheel creep.

BACKGROUND OF THE INVENTION

Traditionally it has been a common practice for locomotive designers tolimit the creepage or slip of the wheels on the rail to approximatelyone percent in order to avoid the condition of total wheel slip whichresults in rail or wheel burn. It was determined later that thewheel/rail contact has considerably more unused capacity to produceadhesion beyond one percent creepage.

An improvement in the locomotive adhesion and traction capacity wasachieved in a second generation control system called the creepagecontrol. In this approach, controlled wheel slip is provided in a waywhich limits the maximum wheel slip and yet allows sufficient slippagefor the wheels to obtain high adhesion. This method is a significantimprovement on the earlier practice and considerably high adhesionlevels have been achieved by using this approach. It has, however,several major disadvantages. These are:

(1) Since somewhat arbitrary creepage limits are used for limiting thepower in the motors, the wheels end up operating in an adhesion creepagedomain which is often unstable, resulting in both mechanical andelectrical instabilities in the system. This will be more clear in laterdiscussions. Therefore, all elements or members of the drive or powertrain starting from the wheels all the way up to the engine includingthe electrical power plant have to sustain sudden changes and shockloading. This can lead to early failure of the weaker links in the drivechain.

(2) The adhesion levels achieved in this method are quite high but notin the optimum region on a continuous basis. In other words,improvements in adhesion levels are still possible.

(3) Creepages larger than necessary lead to wasted energy and fuelconsumption. They also produce higher wheel and rail wear than isnecessary for producing the operating adhesion levels.

(4) There is one other problem with the present control systems. Theyresort to application of sand between the wheel and the rail wheninsufficient adhesion is being produced. There is no indication of theneed for sand application given considerably in advance. Suchindication, if it were available, could enable a rail cleaning systemsuch as in U.S. Pat. No. 4,781,121 to start operating and cleaning therail. This would allow sand application to be avoided in most instances,which is desirable because sand increases wheel/rail wear by ten to onehundred times (see Kumar, S., Krishnamoorthy, P.K. and Prasanna Rao,D.L., "Wheel-Rail Wear and Adhesion With and Without Sand for a NorthAmerican Locomotive", A.S.M.E. Journal of Engineering for Industry, May1986, Vol. 108, pp. 141-147).

The present invention overcomes all the above four difficulties. Ithelps to operate the locomotive wheels in the stable adhesion/creepagedomain. It permits increase of power/generator excitation and wheelcreep only up to certain maximum values which depend on the wheel/railcontact characteristics and by which the fuel consumption is kept low aswell as the wheel/rail wear is kept low. It achieves nearly optimumlevels of adhesion on a continuous basis. It achieves a clear signal inadvance that rail cleaning is needed and activates the cleaning systemfor increased adhesion levels. It also activates sand application whencreep exceeds a certain specified high value and shuts it off when it isnot needed. These factors will become more clear in the later discussionwith the use of figures.

SUMMARY OF THE INVENTION

This invention relates to a new method of controlling locomotive wheelslip for achieving nearly optimum adhesion that can be achieved underthe prevailing wheel/rail surface/environmental conditions while keepingdown wheel/rail wear and associated wasted energy. It reduces the shockloading and resulting damage to the electro-mechanical drive train ofthe locomotive to a minimum, and thus enhances the life of the drivetrain components significantly. It achieves the above by keeping thelocomotive wheel rail contact characteristics stable all the time; hencethe name "Stable Advanced Adhesion System" abbreviated as SAAS in laterdiscussion. This invention is intended to be used on electriclocomotives which are either powered by an on board generator or bywayside electrical power.

A method and apparatus are disclosed for controlling a locomotive wheelslip for achieving nearly optimum adhesion continually when demanded,while keeping down the levels of: wheel rail wear, energy wasted inexcessive wheel slip, and the shock loadings and resulting damage to theelectro-mechanical drive train of the locomotive. The basis of theinvention for high adhesion demand control of a locomotive is to alwaysmaintain a small but positive value of the slope of the wheel-railadhesion creep curve (or differential of adhesion versus creep) for alltraction axles of a locomotive through microprocessor control.

One way of achieving this is to maintain a positive small value of thedifferential of the electric current with respect to rpm for all seriestraction motors of a locomotive. It requires continuous sampling of themotor speeds, currents and voltages and uses the back emf per rpm versusmotor current characteristics of the series traction motors connected inparallel, to compute certain defined functions of current I and ∂I/∂n,e.g. B/n)(∂I/∂n) where n is motor rpm and β is a constant. If the valueof this function is below a certain level for defined values of I, themicroprocessor sends a signal to activate rail cleaning and deactivatesit when the value of the function has reached beyond another specifiedvalue. The value of this function by itself or in conjunction withanother function of I, ∂I/∂n, e.g. (1+(∂I/∂n)²)^(1/2) dn is used todefine an operating window for the control and operation of motorscontinually in the optimum domain when high adhesion is demanded. If therail is so dirty that rail cleaning does not clean it enough (or railcleaning is not available) and creep develops above a specified value,sand application is turned on while monitoring the control functions forcorrecting the generator excitation levels. This control brings theperformance to a low-creep, stable domain and shuts off sanding when itis not needed. When, due to a sudden increase in rail contamination, thevalue of the control function becomes negative, the microprocessorcontrol reduces the generator excitation in stages until the functionbecomes positive and inside the operating window again. Thus operationin the optimum adhesion window is achieved under all rail conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows typical adhesion/creepage characteristics of a locomotiveon a rail with different surface conditions.

FIG. 2 shows a method of locomotive control from one adhesion/creepagecurve to another as rail surface conditions change.

FIG. 3 shows the adhesion-creepage and motor current-rotational speedrelationship for Differential Creepage Control SAAS.

FIG. 4 shows a method to compute the motor rpm n.

FIG. 5 depicts a typical back emf per rpm versus motor current curve fora series wound motor.

FIG. 6 is a block diagram of control for a locomotive including the newdifferential creepage control according to the invention.

FIG. 7 is a brief description of the Differential Creepage Control SAAS.

FIG. 8 shows a voltage/amperage plot of typical motor power changeswithin the generator power bounds.

FIG. 9 shows the five domains of adhesion creepage for locomotivecontrol with SAAS. It also shows the start-up of rail cleaning andsanding.

FIGS. 10 and 11 are a computer flow chart showing the basis ofmicroprocessor implementation of differential creepage control.

FIG. 12 gives the system status description used in the SAAS flow chartshown in FIGS. 10 and 11.

DETAILED DESCRIPTION OF THE INVENTION

Key To Symbols Used In The Following Description:

μ--Percent adhesion coefficient

ξ--Percent creepage

t--Time

I--Motor Current

ΔJ--Increment of motor current

V--Motor Voltage

E--emf

X--Generator Excitation

R--Resistance

R_(W) --Wheel diameter gear ratio related constant

V₂ --Train speed

n--Motor speed (rpm)

Δn--Increase in motor speed corresponding to ΔI increment in motorcurrent at a given speed

Δn_(s) --Value of Δn at which sanding starts

f--Excitation control function (function of dI/dn)

β--A constant used in function f

Φ--Rail cleaning control dI/dn function

Φ_(C) --Value of Φ at which rail cleaning starts

γ₂ --Value of function f at the lower edge K₂ (FIG. 2) of adhesionwindow

γ_(o) --Value of function f in the high adhesion operating domain 5(FIG. 9) and K_(o) in FIG. 2

δ--Variation of γ acceptable for steady operation domain 5 (FIG. 9)

α₁,α₂ --Constants used in control functions

G1--Start rail cleaning constant

G2--Rail cleanliness constant for stopping sanding

G3--Motor speed creep reduction constant

G4--Large step excitation reduction constant for unstable negative sloperegion, domain 4 (FIG. 9)

G5--Large step excitation increase constant for stable positive sloperegion, domain 1 (FIG. 9)

Z--Number of seconds for computer control pause

i--Algorithm control flow connector from FIG. 10 to FIG. 11

ii--Algorithm control flow connector from FIG. 11 to FIG. 10.

Based on extensive field tests of locomotives (see Logston, C.F. andItami, G.S., "Locomotive Friction-Creep Studies", A.S.M.E. JointRailroad Conference, Montreal April 1980), FIG. 1 shows a qualitativeplot of locomotive percentage adhesion versus percentage creepage forthree conditions of rail surface. These are: high contamination 11, lowcontamination 12, and with sand application 13. The peaks of thesecurves have been joined by a dashed line 14 which separates the adhesioncreepage space into two regions: a clear area 15, and a shaded area 16.It is an objective of the present invention to operate the locomotive inthe clear region 15. The shaded region 16 is not considered to be goodto operate in, as it is a region of mechanical and electricalinstability in which the power train components starting from thewheels, all the way up to the engine and electrical power plant have tosustain sudden changes and shock loadings. This can lead to earlyfailure of the weaker links in the chain. Large unstable creepagesassociated with region 16 can lead to torsional oscillation of wheelsets, wasted fuel and higher wheel/rail wear. Moreover, the adhesionlevels achieved in region 16 are obviously not the maximum. The desiredregion of locomotive performance is to the left of the dashed curve 14,with the optimum being very near the peak of the operating adhesioncreepage curve. The dashed curve 14 is a locus of all such peaks. Whenhigh adhesion is demanded of the locomotive, its adhesion/creepagecharacteristics can approach the dashed boundary but should not beallowed to cross it. However, if sometime due to sudden changes in therail surface conditions the dashed boundary is suddenly crossed, afurther objective of this invention is that the controls should adjustthe power in such a way that the characteristics return as fast aspossible to the region 15.

It is a further objective of this invention that when high adhesion isdemanded the locomotive operates at adhesion levels slightly below thepeak and to the left of dashed line 14. The new control system of thepresent invention called "Differential Creepage Control System forLocomotives - A Stable Advanced Adhesion System" is based on the premisethat the first differential of adhesion coefficient with respect tocreepage will stay positive all the time and if it does become negativemomentarily, the control system will adjust power so that it becomespositive again.

FIG. 2 shows how the above objective of operating in region 15 of FIG. 1can be achieved. As the rail surface conditions change, thecorresponding adhesion creepage curve on which the locomotive wheels areoperating also changes. FIG. 2 shows two such curves 17 and 18. Curve 18corresponds to a higher contamination level. For high adhesionapplications the locomotive should operate in the an optimum range,defined herein as adhesion window K₁ K₂, 19 on curve 17 and adhesionwindow K₁ 'K₂ ', 21 on curve 18, these being the desired windows. Thefigure shows the method of locomotive control from one adhesion creepagecurve window to another as the rail surface conditions change. Let usassume that as the train starts from a terminal the rail surfaceconditions correspond to adhesion creepage curve 17. The locomotiveengineer increases the motor excitation level which corresponds to anadhesion level shown in FIG. 2 from P_(o) to P₁. Assuming that highadhesion is demanded with correspondingly high level of locomotive powerbeing available, either the locomotive engineer or amicroprocessor-based control system continues to increase the excitationlevel to increase adhesion from P₁ to P₂, and from P₂ to P₃. Themicroprocessor continually checks values of suitable functions relatedto the differential of adhesion with respect to creepage. During thisprocess if the value of this function falls below a certain specifiedvalue with respect to the current I, the microprocessor sends a signalto activate a rail cleaning system, such as that shown in U.S. Pat. No.4,781,121 and available from Tranergy Corporation of Darien, Ill. undertheir trademark SENTRAEN I. The cleaning continues until the value ofthe adhesion creepage differential function remains below anotherspecified value. It stops when the value of the control function exceedscertain specified limits. Levels of adhesion, creepage and itsdifferential are continually monitored and once the adhesion levels arehigh enough (corresponding to lower end K₂ of the adhesion window K₁K₂), the microprocessor takes control of the generator excitation levelsand increases it in small steps so that the value of the functionreaches a value corresponding to K_(o), the operating value of optimumadhesion, and maintains it within the window K₁ K₂ for steady operation.

There can be a situation when due to sudden degradation of the railsurface condition the locomotive may momentarily operate at anexcitation level C₁ corresponding to adhesion creepage at point C₁ shownin FIG. 2. As soon as the microprocessor checks and determines that thedifferential of adhesion versus creepage or the value of a selectedcorresponding function at that excitation level is negative, it willreduce the excitation power levels in steps to corresponding values forC₁ to C₂ to C₃ and finally land in the adhesion window K₁ K₂ at K_(o) 19as determined by the specified function. FIG. 2 further illustrates theconcept of locomotive wheel rail contact softening with the dashed line19, 20. If the locomotive were operating at excitation levelscorresponding to the window K₁ K₂ and suddenly the rail conditiondeteriorated, the wheel rail contact will suddenly soften and perform atlevel 20. The microprocessor on checking a specified functioncorresponding to adhesion creepage differential finds that it isnegative and implements immediate correction of excitation levels sothat the locomotive wheel performance changes from 20 towards 21 andfinding the specified adhesion creepage differential function to be atthe specified positive value of the function, it computes the locationof the new desired adhesion window K₁ 'K₂ ' and holds the excitationlevels to dwell within that range.

FIG. 2 also shows how a locomotive control will change when its wheelssuddenly encounter a much cleaner rail corresponding to adhesioncreepage curve 17. At the existing excitation levels corresponding toadhesion window K₁ 'K₂ ' and with the change in rail surface conditions,the wheel performance moves to level 22 on curve 17. The microprocessor,upon checking that the adhesion creepage differential function is not atthe specified optimum value, increases the excitation level to make theadhesion reach level K_(o) and controls power for operation within theadhesion window K₁ K₂. The terms used in the description here are listedin the legend box 23. With this differential creepage control system,the locomotive will operate in the desired adhesion windows nearly allthe time (except the unavoidable short durations in which itsperformance jumps into the undesirable region 16 of FIG. 1 and isimmediately corrected).

It is somewhat expensive and difficult to measure on a continuous basisthe differential of adhesion with respect to creepage for all the drivenaxles of a locomotive. The present invention therefore incorporates anew method of measuring and controlling the differential of adhesionversus creepage as shown in FIG. 3. The adhesion coefficient of a singleaxle is proportional to the torque of the motor driving that axle whichin turn is proportional to the current I of that motor. This means thatthe rate of change of adhesion in time Δμ/Δt is proportional to the rateof change of current in time ΔI/Δt, where I is the current and t is thetime (Eqn. 1). The creepage of the wheels ξ is equal to (nR_(W) -V₂)/V₂, (Eqn. 2), where R_(W) is a wheel diameter and gear ratio relatedconstant, V₂ is train speed and n is motor rpm. Differentiating Eqn. 2for a small time increment Δt and neglecting second order terms, we canwrite Eqn. 3, indicating that the rate of change of creepage with timeΔξ/Δ t is proportional to the rate of change of motor rpm Δn/Δt. Thisassumes that the train acceleration is not large, i.e. dV₂ /dt is nearlyzero. For most high adhesion demand applications this condition issatisfied. Equation 3 has another important implication. Increment ofcreep is proportional to increment of motor speed for a given trainspeed and for a small period of time and small accelerations. Thisproportionality will be used later for estimating creep conditions forsanding. Dividing Eqn. 1 by Eqn. 3, we see that the differential ofadhesion with respect to creepage ∂μ/∂ξ is proportional to thedifferential of motor current with respect to motor rpm ∂I/∂n. In otherwords, we conclude that ΔI/Δn can be used for controlling Δμ/Δξ for eachindividual axle. It should be pointed out here that locomotive controlbased on a ∂I/∂n function does not require measurement of wheel diameteras it is changing with wear. Such measurements and calibration arenecessary for some presently used motor rpm based control systems.

FIG. 4 shows a method to compute the motor rpm n. This method may beused if it is not desired to actually measure the motor rpm with themotor speed transducers. It is considered preferable to make actualmotor speed measurement rather than compute the motor rpm. However, ifgreat accuracy of control is not desired, the method of computation willprove less expensive and therefore economically more desirable. FIG. 4shows that the input values of current and voltage I_(N) 24 and V_(N) 25for a particular motor N when combined with the stored information ofthe motor characteristics of back emf per rpm, E/n, versus motorarmature and field current I shown in FIG. 5 will yield the intermediatevalues of E/n and E. These values are derived by using the back emf or Edeveloped from the E/n curve and basic motor equation V=E+IR+V_(b),where V is the total motor voltage, R is the total motor resistance, andV_(b) is the brush drop. (The value of V_(b) is very small and thereforeit may be ignored in the computation). Using this equation and themeasured value of I_(N) 24, and the resistance of the motor 27 andutilizing the summer 28, the value of the back emf E is obtained.Dividing the value of E by E/n 29 yields the value of n 30. Knowing thevalues of I_(N) the motor current and the motor rpm n, the value of(∂I/∂n) can be computed.

Thus, motor current and motor rpm can be chosen as first and secondparameters such that the differential of the first with respect to thesecond is proportional to the differential of adhesion with respect tocreepage. It will be understood that alternatively the adhesion andcreepage could be chosen as the first and second parameters. Thesequantities could be measured directly and the differential used tocontrol the generator excitation as explained above.

FIG. 6 shows a block diagram of control for a locomotive including aDifferential Creepage Control System (SAAS) according to the presentinvention. A diesel engine 31 drives the generator 32 which has a field47 supplied by conventional generator excitation control 46 whichnominally effects a constant horsepower output of the generator 32. Four(or more) series wound motors A 33, B 34, C 35, and D 36 are connectedin parallel across the generator with each motor driving an axle of thelocomotive. There are two sets of transducers on each motor. One setmeasures the motor speeds 39 and the other set measures the motorcurrents 40. If great accuracy of control is not desired or notnecessary, the motor speeds may be computed as shown in FIG. 4. Fordoing this, value of the voltage input V to the four motors is obtainedthrough 37. The current measurements and motor speeds (measured orcomputed) are used through step 41 to calculate ΔI/Δn for all motors 43.The smallest value of ΔI/Δn is identified 42 by the microprocessor,which then uses this value for locomotive control through thedifferential creepage control 43. SAAS performs the following controlfunctions:

(i) When the power is being increased under manual control, it checkswhether the rail requires cleaning. If it does, it turns the railcleaning 44 on. This is done by comparing a specified dI/dn function Φwith I. If and when the value of this function exceeds a certain valuewith respect to I, it shuts off rail cleaning.

(ii) As the power is being increased further while high adhesion isdemanded from the locomotive, and the value of another specified dI/dnfunction f equals a certain specified value corresponding to the lowerend K₂ of the adhesion window (FIG. 2), the computer is given control ofgenerator excitation. The computer maintains this control until thelocomotive engineer manually reduces power/excitation, or applies brakesor goes on manual override.

(iii) Once the operation is in the adhesion window the computer adjustsexcitation levels to maintain operation at the optimum adhesion levelcorresponding to K_(o) in FIG. 2.

(iv) If at any time the largest of the wheel creep levels measured by Δnexceeds a specified value Δn_(s) (a value corresponding to specifiedcreep levels such as 6-8%), sand application 45 is activated by thecomputer. Sand application continues until either n drops below aspecified fraction of n_(s) or the function Φ exceeds a certainspecified value, discussed later.

(v) If at any time dirty rail is suddenly encountered and the dI/dnfunction f becomes negative, the computer reduces the generatorexcitation levels in large steps until the value of f corresponds toadhesion level K_(o) (FIG. 2).

(vi) If at another time clean rail is encountered and f becomes smallerthan the specified value for K_(o) (FIG. 2), the computer increasespower/excitation in steps until the function f reaches the value forK_(o).

FIG. 7 shows the description of SAAS. The microprocessor receives theinput of the motor currents and the motor speed 48 and 49. If, however,the motor speeds are not measured, the motor speeds are computed 50.Based on the readings of motor current and motor speeds, values of aselected ΔI/Δn function are calculated 51. The computer analyzes thevalues of the smallest ΔI/Δn according to an algorithm discussed laterand provides control of power 52 through the motor excitation control.This insures that the locomotive operation is in the optimum ∂μ/∂ξdomain 53. Two suitable ΔI/Δn functions f and Φ (discussed earlier) areselected for the microprocessor control of the locomotive. Severalchoices 54 are shown in FIG. 7 as examples. The preferred function f isβ/n·ΔI/Δn. The preferred function Φ is either the same as function f orαI/n² ·ΔI/Δn. Many other functions can be considered for this purpose.

FIG. 8 shows a typical plot 55 of a DC generator power showing howcurrent in amperes changes with voltage for a given level of power beingproduced by the generator. Qualitative individual motor performancecurves 56 at different speeds and values of adhesion creepage are alsoshown superposed on this plot in FIG. 8. Comparing with FIG. 2 theadhesion creepage levels P₁, P₂, P₃, C₃, C₂, C₁ fall on different curves57 of a motor as shown in FIG. 8. All these levels of adhesion creepageare achievable as long as all the points P₁, P₂, P₃, C₃, C₂, C₁ fallwithin the bound of power 55 generated. If any of the points falloutside the bound, the corresponding value of adhesion creepage will notbe reachable unless the generator power is increased. In other words,the final controlling parameters are the excitation level of thegenerator and the power output capacity of the engine.

FIG. 9 shows an adhesion creepage curve for locomotive performance.There are five domains shown in the curve. Domain₋₋ 1, 58 extends fromzero adhesion level to the lower end of the adhesion window (K₂ in FIG.2). The value of the control function f at this juncture is γ₂. Domain₋₋2, 59, domain₋₋ 3, 60 and domain₋₋ 5, 62 are all in the adhesion window.The operating domain is intended to be in the center of the adhesionwindow and is shown as domain₋₋ 5, 62. Domain₋₋ 2, 59 is below domain₋₋5, 62 and domain₋₋ 3, 60 is above domain₋₋ 5, 62. The value of thecontrol function f in the center of domain₋₋ 5, 62, is γ_(o). Theunstable and undesirable region of wheel operation is domain₋₋ 4 61.

FIG. 9 also shows two other features of SAAS. When the locomotive isperforming in domain₋₋ 1 and if the value of the rail cleaning controlfunction Φ is smaller than a specified value Φ_(c) the rail cleaning isinitiated by the control system 63. If excessive slip develops and largevalues of Δn (greater-than or equal-to Δn_(S) a specified value) arerecorded 64, the SAAS activates sand application to the rail whilesimultaneously reducing excitation levels so that the wheel performancereturns to the adhesion window. High creep levels are indicative ofdirty rail as well as wastage of energy which should be avoided. Theparameters described in FIG. 9 are used later for development of thecomputer control algorithm of SAAS.

FIGS. 10 and 11 show a computer control algorithm for the implementationof SAAS. This program is continually in operation when the engine/poweris on. It monitors the locomotive performance parameters continually.When the train is started, it is operated under the normal control ofthe locomotive engineer by the presently used operational practices. Theprogram keeps monitoring several control parameters, as the train isaccelerating, to determine if and when high adhesion demand is beingmade from the wheel rail contact. When the performance reaches end ofdomain₋₋ 1 FIG. 9, which is the same location as the lower point of theadhesion window (K₂ in FIG. 2), the computer takes control of thelocomotive through the algorithm of SAAS. It should be noted that therail cleaning and sanding are controlled even when the computer is notin control of the locomotive, except during enforcement of emergencyoverride.

The algorithm incorporates two loops, a primary and a secondary loop.The primary loop does all calculations of and maintains control foroptimum generator excitation levels. It also determines the need tostart or stop rail cleaning and/or sanding. The secondary loop 66through 71 checks if the train is moving and whether the excitation hasincreased above zero base to determine when to enter the primary loop.It also turns off the program when engine power is off.

The algorithm starts 65 and after a brief pause of Z seconds 66, all theneeded constants are read 67 from the data files. These include G1, G2,G3, G4, G5, β, γ_(o), γ₂, δ, Δn_(s), R, R_(W), α₁, and α₂. Readings arealso taken of all the variables needed to make calculations 67. Thesevariables include E/n versus I and Φ_(c) versus I. Readings are thentaken 68 of the operating parameters I, n, X, and V. System status andinput/output communication with the locomotive engineer is then provided69. The train movement is monitored 70 with checking of n=0 and X=0.Before entering the primary loop, it also checks 70 whether theemergency override is on. If the answer is Yes, then computer controlcontinues waiting for the train to start moving (or excitation toincrease) in the secondary loop from 66 to 71. The program is stopped ifengine/power is shut down at anytime. If the answer to 70 is No, controlmoves along the path of the primary loop to 73.

At this point the motor rpm n is calculated or measured for all motors;largest Δn for specified ΔI is identified and the smallest value of thefunction f determined. Function Φ is also calculated. Stages 74 through78 check if rail cleaning is necessary, whether the cleaning is notalready on 74 and when Φ<Φ_(c), 75, then cleaning is turned on 76. Whencleaning is already on 77 and Φ is greater than G1 times Φ_(c), 77, thenthe cleaning system is deactivated. If both of the above two conditionsare false, then control drops through to 79.

Next the possible need for sanding is addressed. If corresponding to adefined ΔI increment, |Δn| is greater than a predefined constant Δn_(s),79, the creep is unacceptably high and sanding is initiated 82. If sandapplication is not on 80, the computer control drops to the algorithmcontrol connector 85. If function is greater than G2 times Φ_(c), 81and/or Δn is smaller than Δn_(s) /G3, then sand application is turnedoff 83. A computer algorithm pause is initiated 84 after sandapplication is turned on 82 or off 83 to allow the hardware time torespond to the computer command in order for the next set of readings 68to reflect this change in the locomotive data. The algorithm continuesfrom FIG. 10 to FIG. 11 through page connectors 85 to 87 and 86 to 88.

Computer override is enforced when the locomotive engineer reducesexcitation, starts braking, or demands control from the computer foremergency override. Under normal control operation the engineer cannottake control from the computer to increase power when the algorithm isfunctional. Such power/excitation will be increased in a controlled wayby the computer algorithm only. The locomotive engineer can assumecontrol only through emergency override included in the input/outputstatement 69. If the computer override is on 89, the computer is takenout of control of excitation 90 and continues up to get a new set ofreadings 68. While computer override is on, it is not in control ofexcitation, but it still continues to monitor the parameters. If thecomputer is not in control of the excitation 91 and the control functionf is less than the predefined constant 92, then the microprocessor isput in control of excitation 93. If f is not less than γ₂, thenmicroprocessor control goes back to get a new set of readings 68.

At this point the computer algorithm enters the main sequence of SAAS 94through 102. As shown in FIG. 9, there are five domains of the adhesioncreep curve. Accordingly, there are five sequence control statementscorresponding to each domain. Initially, the algorithm checks if theexisting creep level is situated on the negative side of the creepcurve. This is indicated if the control function f is less than zero 94.This corresponds to domain₋₋ 4 of FIG. 9. In such a case the excitationis decreased, 95, by a large step given by G4*ΔX, where G4 is a constantconsiderably larger than one. If f is less than γ_(o) -δ, 96, then theexcitation is decreased 97 by a small step ΔX. This corresponds todomain₋₋ 3 in FIG. 9. If f is greater than (domain₋₋ 1), 98, excitationis increased, 99 in larger steps by G5* X, where G5 is a constant muchlarger than one. If f>(γ_(o) +δ), domain₋₋ 2, 100, the excitation isincreased by ΔX, 101. If none of the above four conditions 94, 96, 98and 100 are true, then positioning of the locomotive performance in themiddle of the window has been achieved and the microprocessor controldoes not change excitation and goes back to get the next set of readings68. The operation at this point is in domain₋₋ 5 of FIG. 9, 102.

The above algorithm thus achieves rail cleaning when needed, sandapplication when excessive creep develops, computer override, andoperation in the optimum adhesion zone by proper control of excitationof generator.

FIG. 12 gives a description of the system status. It gives an output tothe engineer as to who has control of the locomotive: SAAS or thelocomotive engineer. It gives the status of the emergency override ofthe computer: on or off. It gives the status of the brake system: on oroff. It also gives the conditions of computer override being on or off.It gives the cleaning override system status: on or off, and the sandingoverride status: on or off. And finally, it gives a system check statusas to whether everything is 0.K. or if there is any malfunction.

The preferred adhesion window shown in FIG. 9 is defined as follows. Theupper limit of domain₋₋ 3 is where the differential of adhesion withrespect to creepage is zero. At the center of domain₋₋ 5, thedifferential of adhesion with respect to creepage is about 0.63. At thelower limit of domain₋₋ 2, the differential of adhesion with respect tocreepage is about 1.0 to about 1.5, depending on how tightly themanufacturer wishes to control the locomotive.

It will be understood that the adhesion window could vary from that justdescribed. For example, instead of strictly limiting the function f topositive values, it could be controlled such that small negative valueswould be permitted. In other words, the adhesion window could extendsomewhat beyond the peak of the adhesion-creepage curve.

Whereas a preferred form of the invention has been shown and described,it will be understood that alterations or modifications could be madethereto without departing from the scope of the following claims.

We claim:
 1. A method of controlling power applied to a locomotive drivetrain, comprising steps of:(a) measuring first and second parameters oflocomotive operation, said parameters being chosen such thatdifferential of the first with respect to the second is uniquely relatedto differential of adhesion with respect to creepage; (b) calculating arepresentation of the differential of adhesion with respect to creepage,utilizing the first and second parameters; and (c) adjusting the powerapplied to the locomotive drive train in response to said calculatedrepresentation such that the differential of adhesion with respect tocreepage is within an optimum range defined as an adhesion window andwherein the adhesion window is defined such that within the window thedifferential of adhesion with respect to creepage is greater than zero.2. The method of claim 1 wherein the first parameter is adhesion and thesecond parameter is creepage.
 3. The method of claim 2 wherein theadhesion window is defined such that at its center the value of thedifferential of adhesion with respect to creepage is about 0.63.
 4. Themethod of claim 2 wherein the adhesion window is defined such that atits lower limit the value of the differential of adhesion with respectto creepage is about 1.0 to about 1.5.
 5. The method of claim 2 whereinthe magnitude and direction of the adjustment made in step (c) isdependent on the magnitude and direction of the deviation of therepresentation from the adhesion window.
 6. The method of claim 1wherein the magnitude and direction of the adjustment made in step (c)is dependent on the magnitude and direction of the deviation of therepresentation from the adhesion window.
 7. The method of claim 1wherein the adhesion window is defined such that at its center the valueof the differential of adhesion with respect to creepage is about 0.63.8. The method of claim 1 wherein the adhesion window is defined suchthat at its lower limit the value of the differential of adhesion withrespect to creepage is about 1.0 to about 1.5.
 9. The method of claim 1wherein the adhesion window is defined such that at its lower limit thevalue of the differential of adhesion with respect to creepage is about1.0 to about 1.5 and at its upper limit the value of the differential ofadhesion with respect to creepage is near and greater than zero.
 10. Themethod of claim 1 wherein there is further defined in the adhesionwindow an operating domain having a value of the differential ofadhesion with respect to creepage of about 0.63 at its center and thepower applied to the locomotive drive train is adjusted such that thedifferential of adhesion with respect to creepage is within theoperating domain.
 11. The method of claim 10 wherein the step ofadjusting the power applied to the locomotive drive train ischaracterized by applying a first correction factor to the power whenthe calculated representation of the differential of adhesion withrespect to creepage is outside the adhesion window and applying asecond, smaller correction factor to the power when the calculatedrepresentation of the differential of adhesion with respect to creepageis within the adhesion window but outside the operating domain.
 12. Themethod of claim 1 further characterized in that the locomotive is of adiesel-electric type and the adjustment made in step (c) is effected byaltering an excitation level of the locomotive's generator.
 13. Themethod of claim 1 further characterized in that the locomotive includesa rail cleaning device mounted thereon forwardly of the locomotive drivewheels, and the method further comprises steps of calculating apredetermined function of the adhesion-creepage curve and controllingoperation of the rail cleaning device in response to the value of saidpredetermined function.
 14. The method of claim 1 further characterizedin that the locomotive includes a sand applicator and the method furthercomprises steps of calculating a value representative of the currentwheel creepage and activating the sand applicator when the calculatedvalue of creepage exceeds a predetermined limit.
 15. The method of claim14 wherein the predetermined limit is about 8% creepage.
 16. A controlsystem for controlling power applied to a locomotive drive train,comprising:(a) means for measuring first and second parameters oflocomotive operation, said parameters being chosen such thatdifferential of the first with respect to the second is uniquely relatedto differential of adhesion with respect to creepage; (b) means forcalculating a representation of the differential of adhesion withrespect to creepage, utilizing the first and second parameters; and (c)means for adjusting the power applied to the locomotive drive train inresponse to said calculated representation such that the differential ofadhesion with respect to creepage is within an optimum range defined asan adhesion window and wherein the adhesion window is defined such thatwithin the window the differential of adhesion with respect to creepageis greater than zero.
 17. The apparatus of claim 16 wherein the firstparameter is adhesion and the second parameter is creepage.
 18. Theapparatus of claim 16 further characterized in that the locomotive is ofa diesel-electric type and the means for adjusting the power applied tothe drive train is a generator excitation controller for governing anexcitation level of the locomotive's generator.
 19. The apparatus ofclaim 16 further comprising a rail cleaning device mounted on thelocomotive forwardly of the locomotive drive wheels, and means forcalculating a predetermined function of the adhesion-creepage curve andcontrolling operation of the rail cleaning device in response to thevalue of said predetermined function.
 20. The apparatus of claim 16further comprising a sand applicator mounted on the locomotive, andmeans for calculating a value representative of the current wheelcreepage and activating the sand applicator when the calculated value ofcreepage exceeds a predetermined limit.
 21. The apparatus of claim 20wherein the predetermined limit is about 8% creepage.
 22. A method ofcontrolling the operation of a locomotive of a diesel-electric type andincluding, a rail cleaning device and a sand applicator, comprising thesteps of:(a)d initializing in a microprocessor a set of data defining anadhesion window as the optimum range of locomotive operation on anadhesion-creepage curve, the adhesion window being defined such thatwithin the window the differential of adhesion with respect to creepageis greater than zero; (b) measuring first and second parameters oflocomotive operation, said parameters being chosen such thatdifferential of the first with respect to the second is uniquely relatedto differential of adhesion with respect to creepage, and measuringlevel of generator excitation; (c) calculating in the microprocessor arepresentation of the differential of adhesion with respect to creepage,utilizing the first and second parameters; (d) comparing saidrepresentation of the differential of adhesion with respect to creepagewith the adhesion window to determine if the locomotive is operatingwithin the window; (e) adjusting the lever of generator excitation inresponse to the comparison made instep (d) so as to move the locomotiveoperation into the adhesion window; and (f) successively repeating steps(b) through (e) to maintain the locomotive operation in the adhesionwindow.
 23. The method of claim 22 further comprising steps of comparingthe differential of adhesion with respect to creepage to a predeterminedvalue and operating the rail-cleaning device in response to saidcomparison.
 24. The method of claim 22 further comprising steps ofcalculating a representation of the creepage and comparing saidrepresentation to a predetermined threshold and turning on the sandapplicator when the creepage exceeds the threshold.
 25. The method ofclaim 22 wherein the first parameter is adhesion and the secondparameter is creepage.
 26. A method of maintaining stability in thecontact between a rail and a locomotive drive wheel, with positiveresistance offered by the contact to a slight increase in the torqueapplied to the drive wheel, comprising steps of:(a) measuring first andsecond parameters of locomotive operation, said parameters being chosensuch that differential of the first with respect to the second isuniquely related to differential of adhesion with respect to creepage;(b) calculating a representation of the differential of adhesion withrespect to creepage, utilizing the first and second parameters; and (c)adjusting the power applied to the locomotive drive train in response tosaid calculated representation such that the differential of adhesionwith respect to creepage is within an optimum range defined as anadhesion window and wherein the adhesion window is defined such thatwithin the window the differential of adhesion with respect to creepageis greater than zero.